The present invention relates to a helicopter particularly designed for tactical transport and of the type comprising a front body fitted at the top with a main rotor and, at the rear, with an auxiliary rotor mounted on a tail unit connected integral with the rear end of a tail boom extending rearwards of the rear end of the body.
Here and in what follows, the term `tail boom` is intended to mean a beam connecting the tail rotor and unit to the body of the helicopter, and designed to withstand flection and torque forces originating by the tail rotor and by movable surfaces of the tail unit.
In general, in modern helicopters, the tail boom is a tubular beam supporting the controls for the tail rotor and unit. In case some of these controls are arranged externally of the above tubular beam, they are covered by fairings, which are connected to, but do not form part of, the tail boom.
The construction of a tactical transport helicopter invariably involves a number of major problems, due to the conflicting requirements involved, i.e. maximum carrying capacity of the helicopter, combined with optimum streamlining for improving speed and maneuverability.
On known tactical transport helicopters, the body is usually in the form of an elongated rectangular parallelepipedon, whereas the tail boom is usually in the form of a truncated cone tapered towards the rear end, from which project two separate solids constituting an upper and a lower fin.
The aforementioned known design provides for greater carrying capacity and strength of the helicopter, but only at the expense of reduced streamlining efficiency, both during flight and, especially, when hovering. In fact, when hovering or flying at low/medium speed, the air flow generated by the main rotor clings to the outer lateral surface of the body and, especially, of the tail boom, thus resulting in detachment swirl, in turn, resulting in a relatively high fictitious load distributed along the helicopter and normally referred to as "down load" resistance. This not only reduces the carrying capacity of the helicopter, but also affects its vertical stability.
Furthermore, known helicopters of the aforementioned type also present lateral resistance and, consequently, relatively poor lateral stability, owing to the truncated-cone shape of the tail boom and the relatively small lateral fin surfaces.